FreeBSD Ports -- References

The
Porter's Handbook is the master reference for both creating new
ports and maintaining existing ports, including a section on
Keeping Up. It also contains more detail about the topics below, as
well as more references for further study.

FreshPorts.org is a
valuable tool for further information about individual ports,
such as current version, last checkin, and many other useful
statistics. You may subscribe to a mailing list to get the
latest information about your favorite ports.

The
Web Interface to the Source Repository
allows you to browse the files in the source repository. Changes
that affect the entire port system are now documented in the
CHANGES file.
Changes that affect individual ports are now documented in the
UPDATING file.
However, the definitive answer to any question is undoubtedly to read
the source code of
bsd.port.mk, and associated files.